Electric/magnetic field sensor

ABSTRACT

A UNLV novel electric/magnetic dot sensor comprises: a loop of conductor having two ends to the loop, a first end and a second end; the first end of the conductor seamlessly secured to a first conductor within a first sheath; the second end of the conductor seamlessly secured to a second conductor within a second sheath; and the first sheath and the second sheath positioned adjacent each other. The UNLV novel sensor can be made by removing outer layers in a segment of coaxial cable, leaving a continuous link of essentially uncovered conductor between two coaxial cable legs.

RELATED APPLICATION DATA

This Application claims priority from U.S. Provisional Application No.60/605,069, filed Aug. 27, 2005

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and may havethe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms ofDE-FG02-00ER45831 awarded by the Department of Energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The embodiments of the present invention relate to sensors for measuringmagnetic field and electric field phenomena at the same time at the samepoint in space.

2. Background of the Art

Conventional small magnetic field sensors (commonly referred to asB-dots) consist of a coaxial cable with a coil located at the cable end.The center wire of the coaxial cable extends beyond the outer shield andis shaped in the form of a coil. Typically, the coil may be a singlehalf loop, an integer number of loop turns, or an integer number of halfloop turns. The coil end is then typically soldered to the outer shield.A conventional differential B-dot makes use of two nearly identicalcoils spaced closely together in a nearly unique orientation. Forpackaging purposes, the differential B-dot is housed within a conductiveblock filled with a dielectric substance. This packaging is notnecessary in the differential B-dot design except when trying toeliminate or control proximity effects. Interconnection is made with twoindividual pieces of transmission line (coaxial cables). The B-dot isused to measure the rate of change of the magnetic fields in thelocation of the loop. According to Faraday's law, as the magnetic fieldlines threaded through the B-dot loop changes with respect to time, avoltage is induced in the coil that in turn drives a coil current. In anapproximate sense, the induced voltage is proportional to the number ofloops, the area of the loop, the magnetic field strength and either theinverse of time duration of the change or the time harmonic frequency ofthe signal.

More specifically, the voltage induced in a coil is proportional to thefrequency of the event, the total-cross section of the coil and thenumber of turns. Thus, to obtain reliable sensitivity at lowerfrequencies, it is necessary to increase the cross-section and/or thenumber of turns. On the other hand, to widen the response to highfrequencies, it is necessary for the coil to have low stray capacitances(capacitance between the coil and external entities) and low internalcapacitances (capacitance between coil turns). Consequently, a reducednumber of turns is desired and the dimensions of the sensor should besmall compared with the wavelength corresponding to the highestfrequency of interest. Therefore, it is difficult to fabricate a sensorhaving a wide pass band and with reliable sensitivity throughout thepass band.

A shielded flat coil is also known in the art. The shield is notcontinuous thereby avoiding a short-circuit loop which would generate acurrent in response to changes in the external magnetic field. Thiscurrent would just counter the effects of the external field that theinternal sensor would not detect the external field. A flat coil sensorcan be optimized either for reliable sensitivity at low frequencies witha large diameter and a large number of turns, or for a response at highfrequencies with a small diameter and a small number of turns.Unfortunately, the first optimization leads to a poor response at highfrequencies while the latter optimization leads to a limitation of thesensitivity at low frequencies. Capacitive coupling from shield toshield across the gap exposing the sensor offers limitations to thesensitivity of this device.

The differential B-dot probes currently used to measure B field andexclude the E field are three-dimensional loops. This probe is a matchedseries parallel combination of loops which match a 50 ohm input of atuned receiver or a power meter. This type probe must be constructedutilizing double sided flexible printed circuit board with low lossdielectric. This material is necessary to implement the complexstripline matching networks. In addition, the assembly of these loopsare extremely difficult, time consuming, and the probes are difficult tomaintain. The required power meters and receivers utilized to measurethe output of these type loop probes are very expensive and hard to usefor remote field measurements.

Two dimensional double gap detected probes are used to measure B fieldsin large test volumes which are remote from electrical power. Due to thelarge number of measurement points required to map test volumes andremoteness of some areas of interest, the probes need to be portable. Inaddition, the probe must be small and non-perturbing to the field beingmeasured. The probe described in this disclosure is small, portable, anddesigned for minimum field perturbation. The output of the probe is readby an ordinary high impedance volt meter, which is inexpensive, small,easily portable, and does not require external power. These B-dotsensors may operate by oscillating a B-field in the loop area to inducea voltage in the conducting loop given by the relationship V=A dB/dt,where V is the voltage output of the loop, A is the area of the loop anddB/dt is the derivative of the time varying B-field. This voltage may beDC shifted by the high frequency voltage doublers and filtered by lowpass filters, as described in U.S. Pat. No. 4,647,849. The DC outputs ofthe low pass filters are summed together by semiconductor line andbrought out of the field by semiconductor lines to a voltmeter having acapacitor across it. The semiconductor lines are used to minimize thefield pick-up in the transmission lines as well as minimize fieldperturbations.

U.S. Pat. No. 4,626,791 (“the '791 patent”) discusses B-dots and theirapplications. More specifically, the '791 patent recites that a B-dotsensor may act as a microwave detector. In such an embodiment, thesensor comprises a conducting metal loop placed in a microwave signalenvironment such that magnetic flux passing through the loop changesover time and induces an electrical signal which is then recorded. The'791 patent specifically mentions the inherent limitations of B-dotloops (column 1-2, lines 50-68, 1-9; column 4, lines 46-57). That is,they are designed to only respond to the magnetic flux. However, as setforth above, the magnetic flux is often accompanied by a voltagedistribution within close proximity of the loop The spurious signalsinterfere with the measurement process. The '791 patent suggests the useof a second B-dot loop oriented in the opposite direction from the firstB-dot loop to eliminate the impact of the noise. According to thepresent inventors, the second B-dot loop will have the same amplitudeand 180° phase difference. Therefore, the electric field terms reduce tozero and the magnetic signal is increased by a factor of two. Inprinciple this is reasonable but in practice, for exact cancellation onerequires (this assumes that the coil end is terminated on the groundingshield): 1. Identical probes, 2. Identical relative ground line geometrythat includes line lengths, bends and twists in the line, linecross-sectional dimensions, line orientations, 3. Line and coillocations must be in close proximity (typically 1/40 of the smallestwavelength associated to the highest frequency in the band pass, 4.Coils must have exact relative 180° orientation, 5. Coils and lines mustbe immersed in identical mediums and have identical proximity toexternal structures and 6. Coil axis must be aligned. Deviations fromthese exactness result in spurious noise signals that may effect theoverall measurement especially as the frequency is increase.

U.S. Pat. No. 4,305,705 describes a sensor to provide information aboutflux changes in a coil that encloses a region of changing magnetic fluxis formed by placing a pair of bifilar windings in the plane of the coilfor which flux change is to be sensed. The winding may be inside oroutside the coil. The bifilar winding is placed along that coil, one endof the bifilar winding is terminated in a short circuit and each windingis brought out to voltage-measuring equipment at the other end. Thebifilar winding limits the response to the flux produced by the coilnear which it is disposed and discriminates against changes in magneticflux enclosed within the inner diameter of the coil. Pairs of bifilarwindings may be used to compare differences of voltages, and thewindings may be limited to part of the circumference of the coil to makelocal readiness. This Patent describes a B-dot coil in FIGS. 2 and 3 asa top view and a sectional side view of an EF (equilibrium field) coil18 of FIG. 1. FIG. 3 is a sectional view along section lines 3-3 of FIG.2. FIGS. 2 and 3 of this Patent also show a sensor 20 that is placednext to and inside EF coil 18 and a second sensor 22 placed next to andoutside EF coil 18. Coils such as sensors 20 and 22 are frequentlyreferred to as “B-dot” coils to indicate that they respond to the timederivative of the magnetic flux density B.

SUMMARY OF THE INVENTION

A dot sensor comprises: at least one single half loop, a single wholeloop, multiple whole loops or multiple half loops of conductorseamlessly connected to central conductor materials in two coaxialcables. The dot sensor may have the loops are covered or uncovered witha dielectric material. The dot sensor may have the least one loop (orhalf loop) as a continuation of the two coaxial cables.

Accordingly, one embodiment of the present invention comprises theutilization of a single loop or multiple loops of wire with or without auniform dielectric coating seamlessly attached to two identical coaxialtransmission lines of same length. Near and at the coil end, the outershield of the two coaxial lines are grounded together typically withsolder. Because the shield is not electrically connected to the loopwire, signals pick-up by the shield are minimally coupled into thecoaxial line. Consequently, the structure is substantially symmetric,thereby increasing the effectiveness of differential signal processingto extract the desired signal. The resultant symmetry provides a nearperfect balance of the coil and interconnection structure. Accordingly,the symmetry allows one signal to be subtracted resulting in a zero forcommon mode electric field stimulus. The symmetry also provides amaximum signal for suitably oriented magnetic field energy. Moreover,adding the signals (instead of subtracting the signals) removes themagnetic field stimulus from the combined signal signature leaving theelectric field signal as the measurable. Consequently, the reduction andcontrol of the induction and capacitance expands the useful widebandwidth in the frequency domain.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates a magnetic field sensor of the prior art, and

FIG. 1B illustrates commonly used magnetic sensors in industry andresearch (Note: Multiple loops are typical, only half loop shown)

FIG. 2 illustrates one embodiment of a magnetic field sensor accordingto the present invention.

FIG. 3 shows an end view of a typical coaxial cable. FIG. 4 shows amodified UNLV novel sensor having a pair of loops. In this example, theloops are joined at a central point of symmetry between the two loops.This patent also includes the same geometry without joining at thecentral point of symmetry between the two loops. Such a sensor is adirectional sensor.

FIG. 5 shows a side view of the nearly formed B-dot construction of thepresent technology. (NOTE: Half loop design shown, but multiple loopsare also covered in the disclosure).

FIG. 6 shows a modified UNLV dot sensor having a pair of loops joined ata central point of symmetry

DETAILED DESCRIPTION

A conventional differential B-dot makes use of two nearly identicalcoils spaced closely together in a nearly unique orientation. Forpackaging purposes, the differential B-dot is housed within a conductiveblock filled with a dielectric substance. This packaging is notnecessary in the differential B-dot design except when trying toeliminate or control proximity effects. Interconnection is accomplishedusing two pieces of transmission line one for each dot in thedifferential B-dot set. However, under close scrutiny, the standard anddifferential B-dot reveals critical limitations. The standard B-Dotsuffers from symmetry and ground loop issues. For the differential B-dotto exhibit a spurious noiseless signal, one requires (this assumes thatthe coil end is terminated on the grounding shield): 1. Identicalprobes, 2. Identical relative ground line geometry that includes linelengths, bends and twists in the line, line cross-sectional dimensions,line orientations, 3. Line and coil locations must be in close proximity(typically 1/40 of the smallest wavelength associated to the highestfrequency in the band pass), 4. Coils must have exact relative 180°orientation, 5. Coils and lines must be immersed in identical mediumsand have identical proximity to external structures and 6. Coil axismust be aligned. Deviations from these exactness results in spuriousnoise signals that may effect the overall measurement especially as thefrequency is increase. The embodiments of the present invention overcomethe shortcomings of the prior art. The present invention will beidentified as the UNLV novel dot, novel dot or UNLV dot below since theinvention measure both the electric and magnetic field components at thesame time at the same location in space with a single probe.

In conventional terminology, B means magnetic flux density and D implieselectric flux density. The term “dot” has two implications. First, dotimplies small. Typically, B-Dots and D-Dots as well as UNLV's novel dotmeasures the field at a localized position in space. Second, the dots(B, D, and UNLV's) actually do not measure the fields. What is measuredis the change in the field with respect to time. The fields are obtainedby integrating the signals with respect to time. So, more correctly, thedots measure the rate of change of the field with respect to time. Byappropriately adding and subtracting the output signals the UNLV dotwill provide information on the change in electric and the change in themagnetic fields both with respect to time. After processing the signals,one may recover the actual fields within the bandwidth limitations ofthe device.

Conventional B-Dots and D-Dots find application in the Pulsed PowerIndustry. In the United States, the pulsed power community is small andthe pulsed power industry is driven mainly by the Department of Energyand the Department of Defense. Internationally, the pulsed powerindustry finds applications in the environment, biological/medical andmaterial fields. Conventional Dots also can be characterized as:

-   -   a. Outer shield acting as a signal pick-up so dot is not        shielded.    -   b. Soldering is required to attach the shielded central wire of        the coaxial cable of the conventional to the outer shield. Refer        to FIG. 1 b. [    -   c. Not symmetric, which may affect the interpretation of the        signals measured.    -   d. May require two dots to make a suitable measurement (B-Dot        arrangement) hence size, shape, location, and orientation        affects the meaning of the data measured.    -   e. Measures either the change in magnetic field or the change in        electric field, not both.    -   f. May be considered as being matched since probe is        manufactured from conventional coaxial cables.    -   g. There is a question as to Bandwidth limitations on each        separate design. The bandwidth acceptability is both design and        designer dependent.        The novel technology for UNLV novel dots described herein has        been shown to be capable of providing characteristics such as        being:    -   h. May be considered as being matched since conventional coaxial        cable is used in the design of the sensor    -   i. Provides a relatively wide bandwidth.    -   j. The system is capable of making two measurements at one point        in time at one point in space (depending on the set-up: time        varying magnetic field and a time-varying electric field OR a        time-varying surface current density and a time-varying        voltage).    -   k. The Single B-Dot according to the presently described        technology can perform as a differential B-Dot and as a D-Dot.    -   l. Although functioning as a D-dot, D-dot measurement may be        device specific and may require some calculation or calibration        in the system where measurements are being made.    -   m. The system is naturally a Shielded dot.    -   n. There is no need for solder connections.    -   o. The system has Symmetry.    -   p. The novel B-dot allows for measuring signal transitions from        open circuit to short circuit to be examined with highest        accuracy at each instant in time at a particular location    -   q. The simplicity of the design allows the UNLV novel dot to be        reasonably reproducible.

In the commercial industry, B-Dots have close similarity to loopantennas (Refer to FIG. 1 a). It is well known that loop antennas,especially small loop antennas (dots), are inefficient radiators(transmitters). Small loop antennas find applications as good sensors.

Conventional B-dots have the inner wire of a conventional coaxial cablesoldered to the outside shielding (A coaxial cable is basically acylindrical tube with a wire on tube axis. The region between theoutside radius of the solid wire on axis and the inside radius of theouter tube is filled with an insulator [dielectric].). Refer to FIG. 1b. By an electrostatic effect, a displacement current effect and/or aFaraday effect, a signal can be induced on the outer shield of the wirewhich in turn is fed to the center wire on top of the signal to bemeasured. These are usually undesired effects. In practice, engineersand scientists use two “identical” dots with the “opposite” orientationat “nearly the same region” in space to pick-up hopefully the samesignals. If this can be performed accurately, then the differencebetween the signals picked-up yields the raw data for the time varyingmagnetic field at the coil end. At a high frequency, say greater than 3GHz, the distance between the two dots must be no larger than 2.5 mm inorder to say that the two dots are “feeling” the same signals at thesame time. (Computation was obtained by assuming the dot is in freespace and 1/40 of the wavelength is a small enough engineeringapproximation for both dots to see about the same phase of the wave.)When two B-dots are used in a set to measure the change in the magneticfield while minimizing the so called “capacitive coupling effects” whichwe will denote at the noise or undesired signal effects, the sensor islabeled as a Differential B-Dot. Conventional B-dots also have anon-symmetric geometry about dot center. In the commercial industry, onewould have to use two dots in order to perform a single function inmeasuring the magnetic field or, if appropriate, the surface current. Itwould be hard to develop a probe with this capability especially sinceone wants small compact geometries to reach hard to get at localizedpoints in a system (e.g., an electronic circuit board with manycomponents).

The geometry of the presently described Dot is very simple. In essence,it is a coaxial cable that is commercially found on the market alreadydesigned with conventionally accepted characteristic impedance. Thecharacteristic impedance may be considered as being the loading effectof the medium to transport energy from one point in space to a secondpoint in space without reflection along the line or if you like alongthe cable. For example, free space has a 377 Ohms load to an antenna. Inmost cases, the loading effect of the line to propagating waves is 50Ohms. The coaxial cable is composed of concentrically oriented, solid,cylindrical conductive wire with a cylindrical grounding jacket (tube).The grounding jacket may be a solid copper tube or interlaced strandedwires forming a cylindrical tube. Because it is a readily availablematerial and design, it has been used as the solid copper tube geometryin most studies. Sandwiched in between the (preferably copper)conductors is a dielectric (good electrical insulator). The geometry andmaterials employed in the design of the coaxial cable provides theloading effect of the cable to propagating waves (characteristicimpedance).

In essence the novel dot is formed from a single coaxial cabletransmission line that is commercially found on the market alreadydesigned with conventionally accepted characteristic impedance. Thecoaxial cable is composed of concentrically oriented, solid, cylindricalwire with a cylindrical grounding jacket (tube). The grounding jacketmay be a solid copper tube or interlaced stranded wires forming acylindrical tube. Sandwiched in between the copper conductors is adielectric (good electrical insulator). The geometry and materialsemployed in the design of the coaxial cable provides the loading effectof the cable to propagating waves (characteristic impedance). In thedesign of the UNLV Dot, the coaxial cable shield (the outer coaxialtube) of a predetermined length of coaxial line is carefully cut withoutsignificantly cutting into the dielectric material. A lathe or anypulling apparatus may be used to pull on the ends of the cable piece.With proper pressure on the ends, the outer jacket will slide along thedielectric. Heat applied to the outer jacket may help the outer jacketslide along the dielectric surface. Care must be taken not overheat thecable piece. Once a predetermined length of dielectric is exposed, thecentral portion of the coaxial piece is formed into a single half loopor an integer number of loops or an integer number of loops plus a halfloop so that there is a high degree of symmetry when rotating the dotabout the cable ends 180 degrees. The copper jackets (copper shield) arenot part of the loop. The edges and length of the copper jackets arebrought together and soldered from the edge back a short distance. Theends of the coaxial cable are then appropriately cut and prepared forsuitable connector (SMA, BNC, or etc. depending on the bandwidth)crimping. The dot has now been designed. The dielectric shielding may bestripped from the wire loop using heat and chemical solvents.

The dot is then calibrated with a UNLV dot test stand over a widefrequency range in the frequency domain. A thesis has been devoted tothe study of this test stand and a paper has already been submitted forreview for journal publication. The theory coupled with the test standhardware is unique with reasonable agreement shown between theory andexperiment.

Reference is now made to the figures wherein like parts are referred toby like numerals throughout. FIG. 1 a illustrates a magnetic fieldsensor 50 and corresponding connector 75 found in the prior art. Thissensor is normally considered as a loop antenna. FIG. 1 b illustrates acommonly found B-dot commonly used in research.

Now referring to FIG. 2, the UNLV novel sensor of the present inventionis denoted by reference numeral 100. The sensor 100 includes twotransmission lines 110 each having a connector 120 at a first endthereof. A second end of each line 110 supports one end of a loop ofconductive material 130 for facilitating the measurement of magnetic andelectrical fields. The connectors 120 permit the field sensor 100 tocommunicate with equipment or devices for recording, calculating and/ordisplays data received by the sensor 100.

In free space, the novel dot 100 acts as a dual magnetic flux andelectric flux sensor. Thus, when the UNLV dot 100 is inserted into acavity, it measures the magnetic flux at the point of insertion definedby the area (e.g., 1 mm²) of the actual loop 130. In addition, wheninserted in the plane of a guided structure's metallic boundaries, thesurface current in the nearby conductive surface can be directlymeasured with the dot sensor 100.

The novel dot sensor 100 will have a broad impact in the commercialarena. The sensor 100 may be used as a physics tool or a non-contactfield probe. As physics instrument, the sensor 100 provides insight intothe detailed and accurate behavior of electric currents and theirassociated magnetic flux and can show real-time and fine time (e.g., 20ps) behaviors. Thus, the UNLV dot sensor 100 is useful in situationsinvolving high speed activities. Moreover, the small defined area andsymmetry of the loop 130 provides a sensor for showing behaviors atsmall discrete points. In this manner, arrays of the novel dots can bestrategically placed to detect the movement of energy over largestructures. For example, energy can be sensed in time and space byutilizing multiple UNLV dot sensors 100 along drift regions of linearaccelerators or similar structures.

As a non-contact field probe, the UNLV dot sensor 100 functions like aprobe. That is, the user connects the UNLV dot sensor 100 to anoscilloscope, spectrum analyzer or any other instrument to sample thespatial and time fields being displayed by the instrument. Probes havingultra-wide bandwidth routinely sell for several thousand dollars.Moreover, the shear number of instruments being utilized provides anenticing market for the low cost sensor 100 of the present invention.

Furthermore, acting as a non-contact probe, the UNLV sensor 100 hasapplications in the semiconductor industry. Since semiconductorstraditionally need to be wired bonded to an electric port to be excitedand measured, the novel dot sensor 100 provides a means to measurewithout the necessity of wire bonding. Also, as a non-contact probe, theB-dot sensor 100 will be able to measure discrete points in a circuit.

Advantageously, the UNLV dot sensor 100 disclosed herein solves manyshortcomings of the prior devices, acts as a both a B-dot and D-Dot andV-dot for measuring fast electric and magnetic fields simultaneously atone location, and is low cost.

Reference to FIGS. 3, 4A, 4B, 5 and 6 will assist in better appreciatingthe technology described herein.

FIG. 3 shows a cross-section of a typical coaxial cable 200 comprisingan insulating outer layer 202, the conductive layer 204, theintermediate dielectric layer 206 and the internal semiconductor layer208.

FIG. 4A shows a side view of a typical coaxial cable 200 comprising aninsulating outer layer 202, the conductive layer 204, the intermediatedielectric layer 206 and the internal central conductor layer 208.Grooves 210 and 212 are shown cut into insulating layer 202 and throughthe conductive layer 204, with minimum damage to the dielectric layer206, only to assure that the central conductor layer 208 is not cut orscored. A volume of the insulating layer 214 is to be removed.

FIG. 4B shows where the volume of the insulating layer (not shown) hasbeen removed and two legs of the coaxial cable 200 have been bent asideto further expose the inside of the coaxial cable 200 here with theconductor layer 204 shown for convenience (it is usually removed in thisstep), dielectric layer 206 and semiconductor layer 208. A gap 220 isshown above a hinged line 222 and below the remaining central part 224of the coaxial cable 200.

FIG. 5 shows a side view of the nearly formed B-dot construction 240,after removal of the insulating layer and conductive layer, leaving onlythe dielectric layer 206 and the central conductor layer 208. The gap220 is still shown above the remaining arms of the coaxial cable 200. Anadhesive or solder patch 241 may be used to secore the two coaxialcables 200 together for physical stability of the loop.

Please refer to FIG. 6 which shows a modified UNLV dot sensor 300 havinga pair of loops joined at a central point of symmetry 302 between thetwo loops 304 and 306. The loops need not be joined electrically joined,but they may be so joined. The four arms of coaxial cable 200 are shown,with one pair supporting each of the loops 304 and 306. Othercombinations of multiple loops (e.g., parallel loops, a helical loopwith the coils of the helix being nearly uniformly distant from a commonaxis of the coil, and the like) may also be used.

It can be seen that the B-dot described herein can be simplymanufactured from existing materials to provide a significantlyadvantageous component. As shown in the above description, no solderingwas needed on the functional end of the UNLV novel dot, a symmetricalB-dot can be provided by rounding the loop of central wire of thecoaxial cable, which can be accomplished by simple physical means suchas a shaping center piece in the gap. It is possible to manufacture asimilar B-dot by other means such as providing two cut ends of coaxialcable and securing a loop of semiconductor between the two exposed endsof semiconductor from the two cut ends of coaxial cable. The securing,however, is likely to be by sintering, fusing, or soldering, whichcomplicates the process, makes it more expensive, and reduces some ofthe quality characteristics of performance from a symmetrical,unsoldered loop and arms.

Although the invention has been described in detail with reference toseveral embodiments, additional variations and modifications exist andthe invention should not be limited to any specific embodiment disclosedherein.

1. A B-dot sensor comprising: a loop of sensor conductor having two endsto the loop, a first end and a second end; the first end of the sensorconductor secured to a first central conductor within a first sheath;the second end of the sensor conductor secured to a second conductorwithin a second sheath; and the first sheath and the second sheathpositioned adjacent each other.
 2. The B-dot sensor of claim 1 whereinthe first end of the sensor conductor is secured by being a continuationof the first conductor.
 3. The B-dot sensor of claim 2 wherein thesecond end of the sensor conductor is secured by being a continuation ofthe second conductor.
 4. The novel dot sensor of claim 1 wherein theloop at the end of the coaxial cable, the first coaxial cable and thesecond coaxial cable consists of a single continuous elongated conductorcomprising the sensor conductor.
 5. The novel dot of claim 4 wherein thesensor conductor between the first conductor and sensor conductor has adielectric shield.
 6. The novel dot of claim 4 wherein the sensorconductor between the first conductor and sensor conductor has nodielectric shield.
 7. The dot sensor of claim 4 wherein the first sheathcomprises outer layers of a coaxial cable with the first conductor beingthe center layer in the coaxial cable.
 8. The novel dot sensor of claim4 wherein the second sheath comprises outer layers of a coaxial cablewith the second conductor being the center layer in the coaxial cable.9. The B-dot sensor of claim 7 wherein the second sheath comprises outerlayers of a coaxial cable with the second conductor being the centerlayer in the coaxial cable.
 10. The B-dot sensor of claim 7 wherein anend of the coaxial cable distal from the loop has an electricalconnector thereon.
 11. The B-dot sensor of claim 9 wherein an end ofeach coaxial cable distal from the loop has an electrical connectorthereon.
 12. The B-dot sensor of claim 1 wherein the loop is circular.13. The B-dot sensor of claim 7 wherein the loop is circular.
 14. TheB-dot sensor of claim 9 wherein the loop is circular.
 15. The B-dotsensor of claim 11 wherein the loop is circular.
 16. The B-dot sensor ofclaim 1 wherein the loop is helical.
 17. The B-dot sensor of claim 7wherein at least two loops from two sets of sheaths intersect at anintermediate point and the two loops are secured.
 18. The B-dot sensorof claim 17 wherein the at least two loops are mechanically secured. 19.The B-dot sensor of claim 18 wherein the two loops are electricallysecured together.
 20. The B-dot sensor of claim 18 wherein the two loopsare not electrically secured together.
 21. The B-dot sensor of claim 7wherein the loop is helical.
 22. A method of forming the B-dot sensor ofclaim 1 comprising: providing a coaxial cable comprising in order acentral conductor layer, an adjacent dielectric layer, and a conductorlayer; removing the conductor and the dielectric layer from a centralportion of the coaxial cable; forming a loop of the central conductormaterial while it remains attached to the central conductor layer in thecoaxial cable on both sides of the central portion.
 23. The method ofclaim 22 wherein the coaxial cable also has an outer insulating layer,and the insulating layer is removed from the central portion.
 24. Themethod of claim 22 wherein after removal of the conductor layer and thedielectric layer, the central conductor layer is extended from thecoaxial cable to assist in forming a symmetrical loop of centralconductor.
 25. A dot sensor comprising: at least one single half loop, asingle whole loop, multiple whole loops or multiple half loops ofconductor seamlessly connected to central conductor materials in twocoaxial cables.
 26. The dot sensor of claim 25 wherein the loops arecovered with a dielectric material.
 27. The dot sensor of claim 25wherein at least some loops are free of dielectric material.
 28. The dotsensor of claim 25 wherein at least one loop is a continuation of thetwo coaxial cables.